Knee replacement surgery typically requires the replacement of the distal end of the femur and the proximal end of the tibia. Implant loosening, infection, and device wear are well-documented failure modes of primary knee arthroplasty. In cases where the primary implants fail, a secondary operation (i.e., revision surgery) is required to replace the faulty device. The factors associated with device failure, including infection and osteolysis, often lead to a deterioration of bone quality in proximity to the implanted knee replacement devices. Upon removal of the faulty device, large bone defects are often encountered on both the tibia and the femur. These defects are often characterized by large cavitary voids along with cortical rim defects. Traditionally, treatment of these defects required the removal of a large amount of stable cortical bone to facilitate the implantation of a metal replacement for the bone defect.
Revision knee arthroplasty has existed since the first primary knees failed; bone loss associated with revision surgery is therefore not a new problem. Noiles et. al., U.S. Pat. No. 4,846,839 (“the 839 patent”), discloses a method for affixing a prosthesis to bone that incorporates oval-shaped terraces conforming generically to the anatomy of the proximal tibia. The geometry of the device transfers stresses to the bone in a manner that generally corresponds to the types of stress transfers that occur in natural bone. The 839 patent also states that a coating or roughened surfaces can be applied to the stepped tibial sleeves to improve fixation with the bone.
Blaylock et al., U.S. Published Patent Application No. 200410162619 (“the 619 application”), describe a tibial augment system to replace bone defects that incorporates cone-shaped augments made of a highly porous tantalum material. The intent of the device is said to be minimizing bone loss while providing a stable basis for a tibia tray implant. The device of the 619 application, however, does not appear to incorporate a stepped design, therefore calling into question its ability to transfer stresses from the implant to the bone. In addition, the device of the 619 application does not appear to contain a means for mechanically fixing the tibial tray to the tibial cone augment. Rather, the tibial tray is cemented to the tibial augment that provides for a decreased rotational stability than a mechanical lock.
Although much research has been invested into devices that can be used when a primary knee implant fails, there are still important improvements that are needed. Areas of needed improvements include improved transfer of stresses to the bone in a manner that generally corresponds to the types of stress transfers that occur in natural bone and improved rotational stability.